For building real-time control programs on PC controllers, we designed and implemented a real-time extension library to enhance the Java virtual machine that was already available in the real-time operating system we used. Our extension library has the following advantages: First, the underlying Java virtual machine needs no modification to accommodate it. Second, this extension library is easily ported to any other priority-based real-time operating system. Third, the core of this extension library is basically derived from a subset of the Real-Time Specification for Java (RTSJ) standard, and thus our real-time control program can be moved to a forthcoming RTSJ-compliant Java virtual machine without much difficulty. In brief, our work may help suggest ways of implementing RTSJ, or the notion of (degrees of) ¡§minimal¡¨ compliance/support of RTSJ based on non-RTSJ Java virtual machines. In this paper, we will show the requirement, application programming interface, and implementation of this extension library, and discuss its influence on timing.

Received September 3, 2001; accepted April 15, 2002.
Communicated by Jang-Ping Sheu, Makoto Takizawa and Myongsoon Park.
*A preliminary version of this paper was presented in the 2001 IEEE Canadian Conference on Eelctrical and Computer Engineering (CCECE 2001), Toronto, Canada, May 13-16, 2001. Besides, this research was supported by the National Science Council grant 89-2218-E-009-032, the industry reserach program 89-EC-2-A-17-0285-006 of the ROC Economic Bureau, and the Ministry of Education's Program of Excellence Research 89-EFA04-1-4.